1. Field of the Invention
The present invention relates to a disk apparatus, a head retracting method and a head actuator control circuit for retracting the head for reading/writing a disk to a retract position when a power supply failure occurs.
2. Description of the Related Art
In a magnetic disk drive, a magnetic medium (magnetic disk) is rotated by a spindle motor during operation, where the head is floating on the magnetic medium. If a power supply failure occurs in this state, the head retracting operation is executed. When a power supply failure occurs, power from the power supply to the driver of the VCM for moving the head is stopped, so the energy for retracting the head to be used must be other than that of the power supply.
An example of energy other than the power supply is using the rotation energy of the spindle motor as power to drive the VCM and to retract the head (SPM BEMF rectification), or retract power in a storage battery including a capacitor when power is ON, and driving the VCM and retracting the head using this when the power is shut off.
The former method is a mainstream method that is often used at present. The latter method, which uses not the rotation energy of the spindle motor but electrically converted energy, is used for a disk apparatus which uses a small medium where energy to be stored in the spindle motor is not sufficient.
However the floating height of the head is becoming lower each year as the recording density of disks increases. This is making it difficult to implement both the surface roughness of the CSS (Contact Start Stop) zone to prevent the absorption of the medium and slider, required for the CSS system which is a conventional mainstream system, and the floating of the head slider.
As the means of solving this problem, a head loading/unloading method is used. But for the loading/unloading method, unlike the CSS system, unload operation to climb over the ramp is required just before completely retracting the head. To stably climb over the ramp, approaching the ramp with an initial velocity and force in a predetermined range is necessary.
However, it is possible to predict when a power supply failure will occur. For example, a power supply failure occurs when following up a track in the outer zone of the disk, when following up a track in the inner zone of the disk, or when seeking toward the outer/inner zone, the position of the head and the velocity thereof at this point cannot be specified, but is in a wide range, which makes a stable head retracting (unload) operation difficult.
To solve this problem, the head retracting method shown in FIG. 17 to FIG. 19 has been proposed (e.g. Japanese Patent Application Laid-Open No. H5-54573 (especially, pages 3–4 and FIG. 2)). As FIG. 17 shows, the magnetic disk drive 100 moves the arm 108 including the head using the VCM (Voice Coil Motor) 110 in the radius direction of the magnetic disk 102 which is rotated by the spindle motor 104, and reads/writes the data on a desired track. The ramp (spreader) 106 is disposed at the circumference position of the magnetic disk 102, and the head arm 108 is retracted onto the ramp 106.
The power supply monitor 120 detects the power supply failure and notifies the power supply failure signal POWER SUPPLY FAILURE SIGNAL to the spindle counter electromotive force rectifier 122 and the VCM driver 124. The spindle counter electromotive force rectifier 122 generates power from the counter electromotive force of the spindle motor 104 which is inertia-rotating after the power supply failure occurred, and supplies the power to the VCM driver 124.
The VCM driver 124 supplies a constant current with one polarity (−30 mA) to the VCM 110 for a predetermined time (80 ms) using the timer 126, as shown in FIG. 18, thereby first moves the magnetic head (arm) 108 to the opposite direction (arrow a) from the spreader (ramp) 106 as shown in FIG. 19. Then as FIG. 18 shows, the VCM driver 124 supplies a constant current with opposite polarity (+30 mA) to the VCM 110 for a predetermined time, and then, as shown in FIG. 19, thereby moves the head 108 in a direction to the spreader (ramp) (arrow b) which is opposite of the first direction, to retract the head onto the spreader 106.
In this conventional method, the head is moved to a predetermined position once spending a predetermined time using the current drive function of the VCM driver as is, then the head is moved in the unload (retract) direction with a different predetermined current and predetermined time, so a stable unload operation can be expected if the variation of velocity and position of the head are within a predetermined range.
However with the method of driving the head with a constant current, the current is in proportion to the force and the force is in proportion to the acceleration, so depending on the moving velocity and the position of the head when a power supply failure occurs, it is difficult to guarantee the collision velocity of the head to the inner stop of the arm 108 when the head is driven to the direction opposite from the spreader (ramp) 106, and the head assembly may be damaged.
The velocity of approaching the spreader (ramp) 106 also disperses depending on the moving velocity and the position of the head when a power supply failure occurs, and it is possible that the arm 108 may contact the spreader 106 at high velocity and cause damage to the head assembly. Also it is difficult to design to safely retract (unload) the head with certainty at a velocity which does not cause damage to the head assembly, because dispersion depending on the disk drive is large as a result of the dispersion of external force.